Uncopyrightable The only 15 letter word that can be spelled without repeating a letter is uncopyrightable. uncopyrightable（不可赋予版权的）是唯一个由15个完全不重复的字母组成的单词。

Underground Underground is the only English word that begins and ends with the letters "und." underground（地下的）是唯一一个以und开头又以und结尾的英语单词。